Steric control of dioxygen activation pathways for Mn<sup>II</sup> complexes supported by pentadentate, amide-containing ligands

Parham, Joshua D.; Wijeratne, Gayan B.; Mayfield, Jaycee R.; Jackson, Timothy A.

doi:10.1039/c9dt02682g

Cited by 11 publications

(10 citation statements)

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“…Fe II (Me 3 TACN)(S 2 SiMe 2 ) serves as a platform to activate O 2 to generate a series of Fe/oxygen intermediates (Fe(peroxo), Fe(oxo), and Fe(hydroxo) species), which could be trapped at low temperature and spectroscopically characterized (Scheme and Table ). This sequence of reactive species has been proposed in the activation of O 2 by iron and manganese complexes. ,,− A crystallographically characterized thiolate-ligated Mn III –O–O–Mn III complex has been demonstrated to decay to an oxo-bridged Mn III –O–Mn III ; however, no Mn IV (O) species was identified . In addition, a similar thiolate-ligated Fe complex was shown to react with O 2 to form an Fe III 2 (μ-O) complex.…”

Section: Discussionmentioning

confidence: 99%

Activation of Dioxygen by a Mononuclear Nonheme Iron Complex: Sequential Peroxo, Oxo, and Hydroxo Intermediates

et al. 2019

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The activation of dioxygen by FeII(Me3TACN)(S2SiMe2) (1) is reported. Reaction of 1 with O2 at −135 °C in 2-MeTHF generates a thiolate-ligated (peroxo)diiron complex FeIII 2(O2)(Me3TACN)2(S2SiMe2)2 (2) that was characterized by UV–vis (λmax = 300, 390, 530, 723 nm), Mössbauer (δ = 0.53, |ΔE Q| = 0.76 mm s–1), resonance Raman (RR) (ν(O–O) = 849 cm–1), and X-ray absorption (XAS) spectroscopies. Complex 2 is distinct from the outer-sphere oxidation product 1 ox (UV–vis (λmax = 435, 520, 600 nm), Mössbauer (δ = 0.45, |ΔE Q| = 3.6 mm s–1), and EPR (S = 5/2, g = [6.38, 5.53, 1.99])), obtained by one-electron oxidation of 1. Cleavage of the peroxo O–O bond can be initiated either photochemically or thermally to produce a new species assigned as an FeIV(O) complex, FeIV(O)(Me3TACN)(S2SiMe2) (3), which was identified by UV–vis (λmax = 385, 460, 890 nm), Mössbauer (δ = 0.21, |ΔE Q| = 1.57 mm s–1), RR (ν(FeIVO) = 735 cm–1), and X-ray absorption spectroscopies, as well as reactivity patterns. Reaction of 3 at low temperature with H atom donors gives a new species, FeIII(OH)(Me3TACN)(S2SiMe2) (4). Complex 4 was independently synthesized from 1 by the stoichiometric addition of a one-electron oxidant and a hydroxide source. This work provides a rare example of dioxygen activation at a mononuclear nonheme iron(II) complex that produces both FeIII–O–O–FeIII and FeIV(O) species in the same reaction with O2. It also demonstrates the feasibility of forming Fe/O2 intermediates with strongly donating sulfur ligands while avoiding immediate sulfur oxidation.

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Section: Discussionmentioning

confidence: 99%

Activation of Dioxygen by a Mononuclear Nonheme Iron Complex: Sequential Peroxo, Oxo, and Hydroxo Intermediates

et al. 2019

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“…There are limited reports on isolobal analogues of iron(IV)-oxo species. − However, Borovik and co-workers observed that the iron(III)-imido complexes could be synthesized by intermolecular C–H abstraction by an iron(IV)-species (Scheme ). The system was spectroscopically characterized and crystallographically trapped.…”

Section: Biomimetic Studies On First-coordination Sphere Effectsmentioning

confidence: 99%

Inspiration from Nature: Influence of Engineered Ligand Scaffolds and Auxiliary Factors on the Reactivity of Biomimetic Oxidants

et al. 2021

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Enzymes are highly efficient catalysts in Nature that often react with high stereo-, chemo-, and regioselectivity. Usually, enzymes achieve this selectivity through substrate binding and positioning in the active site. The second-coordination sphere effects (also called noncovalent interactions) position the substrate and oxidant in close vicinity, and their effects include electrostatic interactions, hydrogen-bonding interactions, salt-bridges, and also long-range charge-effects from bound cations and anions. Each of these environmental perturbations can affect the kinetics and selectivity of reactions differently. Over the past couple of years, a variety of biomimetic model complexes have been developed and designed that have a similar first-coordination sphere to mononuclear iron-containing enzymes. However, sometimes the reactivity patterns of the biomimetic models in solution are different from the analogous enzymatic systems, and often the selectivity of the reaction is lost. To understand the functional differences between enzymes and biomimetic models, large catalytic clusters have been developed that incorporate second-coordination sphere effects that influence spectroscopic features as well as reactivity patterns. In this Review, we summarize and highlight recent advances in biomimetic chemistry on the creation and design of iron catalysts and the insights that have been obtained when elaborate ligand features are added, which influence the substrate approach to the catalytic center. We start with a highlight of the axial and distal ligand effects of metal centers and how these can be perturbed by hydrogen bonding as well as steric restraints. The syntheses of the active oxidants through the addition of a proton-donating or -accepting groups to the structure have also been discussed in detail in this article. As shown in this work, second-coordination sphere effects can be useful not only to trap and characterize short-lived intermediates but also to enable high selectivity and specificity of a chemical reaction in analogy to enzymatic systems. These biomimetic models appear highly useful for biotechnological and engineering applications with reasonable turnover numbers and consequently have great potential for the future of stereo-and chemoselective synthetic catalytic reactions.

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“…contrast to acetonitrile [18] . This behavior can be attributed to the nature of the solvent coordination in the metal center, which is stronger in the case of DMF, and prevents the introduction of the O 2 in the coordination sphere of the Mn(II) [17d] .…”

Section: Resultsmentioning

confidence: 94%

“…DMF is a convenient solvent to study O 2 activation because Mn II -(dpaq)(OTf) does not react with O 2 spontaneously in DMF, in contrast to acetonitrile. [18] This behavior can be attributed to the nature of the solvent coordination in the metal center, which is stronger in the case of DMF, and prevents the introduction of the O 2 in the coordination sphere of the Mn(II). [17d] Two oxidation features (p 1 and p 1 0 ) and one reduction feature (p 1 0 0 ) are present.…”

Section: Resultsmentioning

confidence: 99%

Electrochemical Formation and Reactivity of a Mn‐Peroxo Complex Bearing an Amido N5 Ligand

et al. 2022

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Herein we report the electrochemical generation of a mononuclear MnIII(OO) (peroxo) complex supported on a dpaq ligand (dpaq=2‐(bis(pyridin‐2‐ylmethyl)amino)‐N‐(quinolin‐8‐yl)acetamide) for the first time, and its reactivity in N,N‐dimethylformamide. The formation of the MnIII(dpaq)(OO) complex is probed by low temperature electronic absorption spectro‐electrochemistry experiments. An analysis of the reduction of the MnIII(dpaq)(OO) complex is carried out combining cyclic voltammetry and simulations. The involvement of a MnII(dpaq)(OOH) complex is proposed based on CV data and is corroborated by DFT computations.

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Steric control of dioxygen activation pathways for Mn^II complexes supported by pentadentate, amide-containing ligands

Abstract: Steric control of dioxygen activation is demonstrated through O2 titration and isotopic labeling experiments for two Mn(ii) complexes.

Cited by 11 publications

References 70 publications

Activation of Dioxygen by a Mononuclear Nonheme Iron Complex: Sequential Peroxo, Oxo, and Hydroxo Intermediates

Activation of Dioxygen by a Mononuclear Nonheme Iron Complex: Sequential Peroxo, Oxo, and Hydroxo Intermediates

Inspiration from Nature: Influence of Engineered Ligand Scaffolds and Auxiliary Factors on the Reactivity of Biomimetic Oxidants

Electrochemical Formation and Reactivity of a Mn‐Peroxo Complex Bearing an Amido N5 Ligand

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Steric control of dioxygen activation pathways for MnII complexes supported by pentadentate, amide-containing ligands

Abstract: Steric control of dioxygen activation is demonstrated through O2 titration and isotopic labeling experiments for two Mn(ii) complexes.

Cited by 11 publications

References 70 publications

Activation of Dioxygen by a Mononuclear Nonheme Iron Complex: Sequential Peroxo, Oxo, and Hydroxo Intermediates

Activation of Dioxygen by a Mononuclear Nonheme Iron Complex: Sequential Peroxo, Oxo, and Hydroxo Intermediates

Inspiration from Nature: Influence of Engineered Ligand Scaffolds and Auxiliary Factors on the Reactivity of Biomimetic Oxidants

Electrochemical Formation and Reactivity of a Mn‐Peroxo Complex Bearing an Amido N5 Ligand

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Steric control of dioxygen activation pathways for Mn^II complexes supported by pentadentate, amide-containing ligands